The invention relates to liquid crystal nematic substances for electro-optical arrangements for modulation of light, for the reproduction of numbers, signs and images as well as to a method for their preparation.
It is known that various effects occuring in nematic crystalline liquids may be used for electro-optical arrangements (M. Tobias, International Handbook of Liquid Crystal Displays 1975-76, Ovum Ltd. London 1976). The orienting effect of liquid crystals may be exploited for investigations of anisotropic properties of added molecules. Furthermore, special separation effects may be obtained when liquid crystals are used as a stationary phase in gas chromatography (G. Meier, E. Sackmann, J. G. Grabmeier, Applications of Liquid Crystals, Springer Verlag, Berlin-Heidelberg-New York 1975).
A large number of substances are already known which, in principle, may be used for that purpose. (D. Demus in: Kmetz, Willisen: Non-emissive Electro-optic displays, Plenum Press New York 1976, page 4). Presently though, no substance is known whose properties in regard to melting and clarification temperature, dielectric anisotropy, viscosity and chemical stability, satisfy the parameters needed for practical application. In mixtures of substances, particularly eutectic mixtures, it is possible to extend to vastly lower temperatures the field of nematic existence by exploiting the depression of the melting point. In mixtures, furthermore, the parameters needed for electro-optical properties as dielectrical anisotropy, viscosity and double refraction, may be modified and adapted for the varying experimental needs. The condition, of course, is the presence of corresponding components of the mixture. The presently-known components do not exhibit optimal values in respect to the variability of the aforecited properties. The presently-known substituted benzoic acid phenylesters (DD WP 86 26 9; R. Stienstraesser, Z. Naturforsch. 27 b. 774 (1972)); substituted hydroquinone-bis-benzoates (DD WP 108 022 and 108 023); and substituted benzoyloxy-benzoic acid phenylester (Ang. Chem. 84, 636 (1972)) possess undesirably high viscosities, thereby causing disadvantageously high switching-on and -off periods in electro-optical arrangements, especially at low temperatures.
These disadvantages are partly reduced for 4-n-alkylcyclohexanecarboxylic acid-4-subst.-phenylesters (DD WP 105 701) as well as in compounds with a cyclohexane ring that contain three rings (DD WP C 09 K/197 331).
The need for additional components of mixtures still remains in order to be capable of obtaining desired properties by mixing thereof.
The objective of the invention is the creation of new liquid crystal nematic substances with advantageous properties in respect to melting and clarification point, dielectrical anisotropy and viscosity, for their use in electro-optical devices for the modulation of light as well as for the display of numbers, signs and designs and also to methods for their preparation.
The invention is based upon the task to obtain new classes of compounds with liquid-crystalline properties, suitable for practical use by starting with 2- or 3-ring esters respectively by exchanging benzene rings with cyclohexane rings.